U.S. patent application number 17/387305 was filed with the patent office on 2022-07-21 for carbon nanotube fiber having improved physical properties and method for manufacturing same.
This patent application is currently assigned to KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. The applicant listed for this patent is KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. Invention is credited to Seung Ki HONG, Jun Yeon HWANG, Hyeon Su JEONG, Dae Yoon KIM, Nam Dong KIM, Seo Gyun KIM, Bon Cheol KU, Dong Ju LEE, Seung Woo RYU, Nam Ho YOU.
Application Number | 20220227631 17/387305 |
Document ID | / |
Family ID | |
Filed Date | 2022-07-21 |
United States Patent
Application |
20220227631 |
Kind Code |
A1 |
KU; Bon Cheol ; et
al. |
July 21, 2022 |
CARBON NANOTUBE FIBER HAVING IMPROVED PHYSICAL PROPERTIES AND
METHOD FOR MANUFACTURING SAME
Abstract
The present disclosure relates to a carbon nanotube fiber having
improved physical properties and a method for manufacturing the
same. The method according to the present disclosure comprises the
steps of: spinning carbon nanotubes with a purity of 90% by weight
or more to obtain a first carbon nanotube fiber; and heat-treating
the first carbon nanotube fiber at 500 to 3,000.degree. C. under an
inert gas atmosphere to obtain a second carbon nanotube fiber,
wherein the second carbon nanotube fiber has a density of 1.0 to
2.5 g/cm.sup.3.
Inventors: |
KU; Bon Cheol; (Wanju_Gun,
KR) ; HWANG; Jun Yeon; (Wanju_Gun, KR) ;
JEONG; Hyeon Su; (Wanju_Gun, KR) ; YOU; Nam Ho;
(Wanju_Gun, KR) ; KIM; Nam Dong; (Wanju_Gun,
KR) ; KIM; Dae Yoon; (Wanju_Gun, KR) ; LEE;
Dong Ju; (Wanju_Gun, KR) ; KIM; Seo Gyun;
(Wanju_Gun, KR) ; HONG; Seung Ki; (Wanju_Gun,
KR) ; RYU; Seung Woo; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY |
Seoul |
|
KR |
|
|
Assignee: |
KOREA INSTITUTE OF SCIENCE AND
TECHNOLOGY
Seoul
KR
|
Appl. No.: |
17/387305 |
Filed: |
July 28, 2021 |
International
Class: |
C01B 32/168 20060101
C01B032/168; D01F 9/12 20060101 D01F009/12; D01D 5/12 20060101
D01D005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2021 |
KR |
10-2021-0006762 |
Claims
1. A method for manufacturing a carbon nanotube fiber, the method
comprising the steps of: spinning carbon nanotubes with a purity of
90% by weight or more to obtain a first carbon nanotube fiber; and
heat-treating the first carbon nanotube fiber at 500 to
3,000.degree. C. under an inert gas atmosphere to obtain a second
carbon nanotube fiber, wherein the second carbon nanotube fiber has
a density of 1.0 to 2.5 g/cm.sup.3.
2. The method of claim 1, wherein the first carbon nanotube fiber
has a density of 0.6 to 2.3 g/cm.sup.3, and the second carbon
nanotube fiber has a density of 1.5 to 2.5 g/cm.sup.3.
3. The method of claim 1, wherein the carbon nanotubes are
single-walled CNTs, and the heat treatment temperature is 1,000 to
2,100.degree. C.
4. The method of claim 3, wherein the second carbon nanotube fiber
has a carbon nanotube diameter 1.02 to 1.5 times that of the first
carbon nanotube fiber.
5. The method of claim 2, wherein at least a portion of the carbon
nanotubes is graphitized by the heat treatment.
6. The method of claim 5, wherein the carbon nanotubes include 20
to 100% by weight of double-walled carbon nanotubes, and the heat
treatment temperature is 2,200 to 3,000.degree. C.
7. The method of claim 6, wherein the second carbon nanotube fiber
has a specific tensile modulus 2 to 10 times that of the first
carbon nanotube fiber, and the second carbon nanotube fiber has a
thermal conductivity 1.1 to 3 times that of the first carbon
nanotube fiber.
8. The method of claim 7, wherein the heat treatment temperature is
2,500 to 3,000.degree. C.
9. The method of claim 2, wherein the carbon nanotubes include 20
to 100% by weight of the double-walled carbon nanotubes, and the
heat treatment temperature is 1,000 to 3,000.degree. C.
10. The method of claim 9, wherein the carbon nanotubes include 20
to 70% by weight of the double-walled carbon nanotubes, the heat
treatment temperature is 1,000 to 2,100.degree. C., and the second
carbon nanotube fiber has a carbon nanotube diameter 1.02 to 1.3
times that of the first carbon nanotube fiber.
11. The method of claim 10, wherein the heat treatment temperature
is 1,500 to 1,900.degree. C., and the second carbon nanotube fiber
has a specific tensile modulus 1.5 to 5 times that of the first
carbon nanotube fiber.
12. The method of claim 9, wherein the carbon nanotubes include 80
to 100% by weight of the double-walled carbon nanotubes, and the
heat treatment temperature is 2,200 to 3,000.degree. C.
13. The method of claim 1, wherein the carbon nanotubes are
purified by chemical purification.
14. The method of claim 13, wherein the chemical purification
comprises the steps of: (i) treating carbon nanotubes using a
strong acid alone or a mixture of the strong acid and hydrogen
peroxide or ammonium hydroxide (NH.sub.4OH); (ii) removing a metal
catalyst in the carbon nanotubes by gas phase reaction of a halogen
element compound; or (iii) combining them.
15. The method of claim 1, wherein the fiber manufacturing method
is performed by wet spinning, dry spinning, dry-wet spinning, or
liquid crystal spinning.
16. The method of claim 1, wherein the step of obtaining the first
carbon nanotube fiber comprises a step of liquid crystal spinning
or wet spinning a dope containing the carbon nanotubes and a super
strong acid.
17. The method of claim 16, wherein the super strong acid is one or
more selected from chlorosulfonic acid, sulfuric acid, fuming
sulfuric acid, fluorosulfonic acid, trifluoroacetic acid,
trifluoromethanesulfonic acid, fluoroantimonic acid, and carborane
acid.
18. The method of claim 16, further comprising a step of oxidizing
the carbon nanotubes by heating the carbon nanotubes under an
oxygen atmosphere in order to increase dispersion of the carbon
nanotubes in the dope.
19. The method of claim 1, wherein the first carbon nanotube fiber
has a specific tensile strength of 0.50 N/tex or more and a
specific tensile modulus of 50 N/tex or more.
20. A carbon nanotube fiber having a density of 1.0 to 2.5
g/cm.sup.3, a specific tensile strength of 1.0 to 8 N/Tex, a
specific tensile modulus of 200 to 1,000 N/Tex, and a thermal
conductivity of 100 to 1,000 W/mK.
21. The carbon nanotube fiber of claim 20, wherein the carbon
nanotube fiber has a density of 1.5 to 2.5 g/cm.sup.3, a specific
tensile modulus of 300 to 1,000 N/Tex, and a thermal conductivity
of 200 to 1,000 W/mK.
22. The carbon nanotube fiber of claim 21, wherein at least a
portion of the carbon nanotube fiber is graphitized, and has a
specific tensile modulus of 400 to 1,000 N/Tex and a thermal
conductivity of 300 to 1,000 W/mK.
23. The carbon nanotube fiber of claim 21, wherein the carbon
nanotubes of the carbon nanotube fiber include 20 to 100% by weight
of the double-walled carbon nanotubes.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Pursuant to 35 U.S.C. .sctn. 119 (a), this application
claims the benefit of Korean Patent Application No.
10-2021-0006762, filed on Jan. 18, 2021, the contents of which are
all hereby incorporated by reference herein in their entirety.
BACKGROUND OF THE DISCLOSURE
Field of the Disclosure
[0002] The present disclosure relates to a carbon nanotube fiber
having improved physical properties and a method for manufacturing
the same.
Related Art
[0003] Although individual carbon nanotubes have excellent
mechanical properties, electrical properties, and thermal
properties, their practical application is limited due to
dispersibility issues.
[0004] A fibrous carbon nanotube aggregate which exists in a
continuous phase rather than a particle form like individual carbon
nanotubes, that is, carbon nanotube fibers, does not have problems
such as the difficulty of dispersion of carbon nanotubes in the
form of particles, and it has an advantage that it can be used in
various ways by making it in the form of a one-dimensional fiber as
it is or a two-dimensional fabric. Further, since the carbon
nanotube fibers have a density as low as 1/5 of those of metals
such as copper or aluminum, the carbon nanotube fibers are very
effective in manufacturing light and strong materials such as
materials in the field of ultra-light composite materials. However,
despite these advantages, the carbon nanotube fibers have a
disadvantage in that they cannot express physical properties, such
as strength, elastic modulus, and electrical conductivity of
individual carbon nanotubes composing the carbon nanotube fibers,
as they are.
[0005] With the methods for manufacturing carbon nanotube fibers
known to date, physical properties of the carbon nanotube fibers do
not reach a satisfactory level, and improvements are required.
SUMMARY
[0006] An object of the present disclosure is to provide a carbon
nanotube fiber having improved physical properties and a method for
manufacturing the same.
[0007] The object of the present disclosure is achieved by a method
for manufacturing a carbon nanotube fiber, the method comprising
the steps of: spinning carbon nanotubes with a purity of 90% by
weight or more to obtain a first carbon nanotube fiber; and
heat-treating the first carbon nanotube fiber at 500 to
3,000.degree. C. under an inert gas atmosphere to obtain a second
carbon nanotube fiber, wherein the second carbon nanotube fiber has
a density of 1.0 to 2.5 g/cm.sup.3.
[0008] The first carbon nanotube fiber may have a density of 0.6 to
2.3 g/cm.sup.3, and the second carbon nanotube fiber may have a
density of 1.5 to 2.5 g/cm.sup.3.
[0009] The carbon nanotubes may be single-walled carbon nanotubes,
and the heat treatment temperature may be 1,000 to 2,100.degree.
C.
[0010] The second carbon nanotube fiber may have a carbon nanotube
diameter 1.02 to 1.5 times that of the first carbon nanotube
fiber.
[0011] At least a portion of the carbon nanotubes may be
graphitized by the heat treatment.
[0012] The carbon nanotubes may include 20 to 100% by weight of
double-walled carbon nanotubes, and the heat treatment temperature
may be 2,200 to 3,000.degree. C.
[0013] The second carbon nanotube fiber may have a specific tensile
modulus 2 to 10 times that of the first carbon nanotube fiber, and
the second carbon nanotube fiber may have a thermal conductivity
1.1 to 3 times that of the first carbon nanotube fiber.
[0014] The heat treatment temperature may be 2,500 to 3,000.degree.
C.
[0015] The carbon nanotubes may include 20 to 100% by weight of the
double-walled carbon nanotubes, and the heat treatment temperature
may be 1,000 to 3,000.degree. C.
[0016] The carbon nanotubes may include 20 to 70% by weight of the
double-walled carbon nanotubes, the heat treatment temperature may
be 1,000 to 2,100.degree. C., and the second carbon nanotube fiber
may have a carbon nanotube diameter 1.02 to 1.3 times that of the
first carbon nanotube fiber.
[0017] The heat treatment temperature may be 1,500 to 1,900.degree.
C., and the second carbon nanotube fiber may have a specific
tensile modulus 1.5 to 5 times that of the first carbon nanotube
fiber.
[0018] The carbon nanotubes may include 80 to 100% by weight of the
double-walled carbon nanotubes, and the heat treatment temperature
may be 2,200 to 3,000.degree. C.
[0019] The carbon nanotubes may be purified by chemical
purification.
[0020] The chemical purification may comprise the steps of: (i)
treating carbon nanotubes using a strong acid alone or a mixture of
the strong acid and hydrogen peroxide or ammonium hydroxide
(NH.sub.4OH); (ii) removing a metal catalyst in the carbon
nanotubes by gas phase reaction of a halogen element compound; or
(iii) combining them.
[0021] The fiber manufacturing method may be performed by wet
spinning, dry spinning, dry-wet spinning, or liquid crystal
spinning.
[0022] The step of obtaining the first carbon nanotube fiber may
comprise a step of liquid crystal spinning or wet spinning a dope
containing the carbon nanotubes and a super strong acid.
[0023] The super strong acid may be one or more selected from
chlorosulfonic acid, sulfuric acid, fuming sulfuric acid,
fluorosulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic
acid, fluoroantimonic acid, and carborane acid.
[0024] The method may further comprise a step of oxidizing the
carbon nanotubes by heating the carbon nanotubes under an oxygen
atmosphere in order to increase dispersion of the carbon nanotubes
in the dope.
[0025] The first carbon nanotube fiber may have a specific tensile
strength of 0.50 N/tex or more and a specific tensile modulus of 50
N/tex or more.
[0026] The object of the present disclosure is achieved by a carbon
nanotube fiber having a density of 1.0 to 2.5 g/cm.sup.3, a
specific tensile strength of 1.0 to 8 N/Tex, a specific tensile
modulus of 200 to 1,000 N/Tex, and a thermal conductivity of 100 to
2,000 W/mK.
[0027] The carbon nanotube fiber may have a density of 1.5 to 2.5
g/cm.sup.3, a specific tensile modulus of 300 to 1,000 N/Tex, and a
thermal conductivity of 200 to 1,500 W/mK.
[0028] At least a portion of the carbon nanotube fiber may be
graphitized, and may have a specific tensile modulus of 400 to
1,000 N/Tex and a thermal conductivity of 300 to 1,500 W/mK.
[0029] The carbon nanotubes of the carbon nanotube fiber may
include 20 to 100% by weight of the double-walled carbon
nanotubes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is transmission electron microscope (TEM) images for
each heat treatment temperature of the carbon nanotube fibers
manufactured in Comparative Example 1 and Examples 1 to 5.
[0031] FIG. 2 is graphs showing changes in carbon nanotube (CNT)
diameters for each heat treatment temperature of the carbon
nanotube fibers manufactured in Comparative Example 2 and Examples
6 to 10.
[0032] FIG. 3 is graphs showing changes in carbon nanotube (CNT)
diameters for each heat treatment temperature of the carbon
nanotube fibers manufactured in Comparative Example 2 and Examples
11 to 15.
[0033] FIG. 4A and FIG. 4B show changes in carbon nanotube
diameters for each heat treatment temperature of the carbon
nanotube fibers manufactured in Comparative Example 1 and Examples
1 to 5.
[0034] FIG. 5A and FIG. 5B show changes in carbon nanotube
diameters for each heat treatment temperature of the carbon
nanotube fibers manufactured in Comparative Example 2 and Examples
6 to 10.
[0035] FIG. 6A and FIG. 6B show changes in carbon nanotube
diameters for each heat treatment temperature of the carbon
nanotube fibers manufactured in Comparative Example 2 and Examples
11 to 15.
[0036] FIG. 7 is a graph showing changes in strength and elongation
for each heat treatment temperature of the carbon nanotube fibers
manufactured in Comparative Example 1 and Examples 1 to 5.
[0037] FIG. 8 is a graph showing changes in strength and elongation
for each heat treatment temperature of the carbon nanotube fibers
manufactured in Comparative Example 2 and Examples 6 to 10.
[0038] FIG. 9 is a graph showing changes in strength and elongation
for each heat treatment temperature of the carbon nanotube fibers
manufactured in Comparative Example 2 and Examples 11 to 15.
[0039] FIG. 10 is thermogravimetric analysis results of the carbon
nanotubes used in manufacturing of the carbon nanotube fibers of
Comparative Examples 1 and 2.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0040] The present inventive concept described below may have
various transformations applied thereto and may have various
embodiments, and specific embodiments are illustrated in the
drawings and described in detail. However, this is not intended to
limit the present inventive concept with respect to specific
embodiments, and it should be understood to include all
transformations, equivalents, or substitutes included in the
technical scope of the present inventive concept.
[0041] Terms used below are only used to describe specific
embodiments, and are not intended to limit the present inventive
concept. The singular expression includes the plural expression
unless the context clearly dictates otherwise. Hereinafter, terms
such as "comprise" or "have" are intended to indicate that a
feature, number, step, operation, constituent element, part,
component, material, or a combination thereof described in the
specification exists, but it should be understood that the terms do
not preclude the existence or addition possibility of one or more
other features, numbers, steps, operations, constituent elements,
parts, components, materials, or combinations thereof.
[0042] In order to clearly express various layers and regions in
the drawings, the thicknesses are shown to be enlarged or reduced.
Throughout the specification, the same reference numerals are
assigned to similar parts. Throughout the specification, when a
part, such as a layer, film, region, plate, or the like, is
referred to as "on" or "above" other part, it includes not only the
case where the part is directly on the other part but also the case
where another part is in the middle therebetween. Throughout the
specification, although terms such as first, second, etc. may be
used to describe various constituent elements, the constituent
elements should not be limited by the terms. The terms are used
only for the purpose of distinguishing one constituent element from
another.
[0043] Although the terms such as first, second, etc. may be used
to describe various elements, components, regions, layers and/or
areas, it will be understood that such elements, components,
regions, layers and/or areas should not be limited by these
terms.
[0044] Further, the processes described in the present disclosure
do not necessarily mean that they are applied in order. For
example, when a first step and a second step are described, it will
be understood that the first step does not necessarily have to be
performed prior to the second step.
[0045] Hereinafter, a carbon nanotube fiber according to an
embodiment and a method for manufacturing the same will be
described in detail with reference to the drawings.
[0046] A method for manufacturing a carbon nanotube fiber according
to an embodiment may comprise the steps of: spinning carbon
nanotubes with a purity of 90% by weight or more to obtain a first
carbon nanotube fiber; and heat-treating the first carbon nanotube
fiber at 500 to 3,000.degree. C. under an inert gas atmosphere to
obtain a second carbon nanotube fiber, wherein the second carbon
nanotube fiber may have a density of 1.0 to 2.5 g/cm.sup.3.
[0047] The first carbon nanotube fiber may have a density of 0.6 to
2.3 g/cm.sup.3, and the second carbon nanotube fiber may have a
density of 1.3 to 2.5 g/cm.sup.3, or 1.5 to 2.5 g/cm.sup.3.
[0048] The method for manufacturing the carbon nanotube fiber not
only increases the van der Waals force by performing spinning and
coagulation processes of carbon nanotubes with a purity of 90% by
weight or more to secure a bundled first carbon nanotube fiber with
a density of 0.6 g/cm.sup.3 or more, or 0.6 to 2.3 g/cm.sup.3, and
then further increasing the density by minimizing the gap between
the carbon nanotubes through heat treatment, but also enables
strength, etc. to be increased by increasing the diameter of the
carbon nanotubes through heat treatment.
[0049] The number of walls of the carbon nanotubes used for
manufacturing the first carbon nanotube fiber may be 1 to 5. The
carbon nanotubes may further include single-walled carbon nanotubes
(CNTs), double-walled carbon nanotubes (CNTs), multi-walled carbon
nanotubes (CNTs), or a combination thereof.
[0050] The carbon nanotubes used for manufacturing the first carbon
nanotube fiber may include 20 to 100% by weight of the
double-walled carbon nanotubes, and the heat treatment temperature
may be 2,200 to 3,000.degree. C., or 2,500 to 3,000.degree. C. At
this time, the second carbon nanotube fiber may have a specific
tensile modulus 2 to 10 times that of the first carbon nanotube
fiber, and the second carbon nanotube fiber may have a thermal
conductivity 1.1 to 3 times that of the first carbon nanotube
fiber.
[0051] The carbon nanotubes used for manufacturing the first carbon
nanotube fiber may include 20 to 100% by weight of the
double-walled carbon nanotubes, and the heat treatment temperature
may be 1,000 to 3,000.degree. C.
[0052] The carbon nanotubes used for manufacturing the first carbon
nanotube fiber may include 20 to 70% by weight of the double-walled
carbon nanotubes, and the heat treatment temperature may be 1,000
to 2,100.degree. C. At this time, the second carbon nanotube fiber
may have a carbon nanotube diameter 1.02 to 1.3 times that of the
first carbon nanotube fiber.
[0053] The carbon nanotubes used for manufacturing the first carbon
nanotube fiber may include 20 to 70% by weight of the double-walled
carbon nanotubes, and the heat treatment temperature may be 1,500
to 1, 900.degree. C. At this time, the second carbon nanotube fiber
may have a specific tensile modulus 1.5 to 5 times that of the
first carbon nanotube fiber.
[0054] The carbon nanotubes used for manufacturing the first carbon
nanotube fiber may include 80 to 100% by weight of the
double-walled carbon nanotubes, and the heat treatment temperature
may be 2,200 to 3,000.degree. C. At this time, the second carbon
nanotube fiber may have a specific tensile modulus 1.5 to 5 times
that of the first carbon nanotube fiber.
[0055] The carbon nanotubes may have a purity of 90% by weight or
more, and contain impurities such as a metal catalyst in an amount
of 10% by weight or less. That is, the carbon nanotubes may contain
the impurities in an amount of 10% by weight or less based on the
total weight of the carbon nanotubes containing impurities. If the
amount of the impurities in the carbon nanotubes is greater than
10% by weight in the process of manufacturing the first carbon
nanotube fiber, dispersibility is lowered so that fiber spinning is
difficult, and impurities such as a residual metal iron catalyst
remain inside the fiber even after spinning so that strength and
electrical conductivity of the fiber may be deteriorated. Further,
mechanical properties of a finally obtained carbon nanotube fiber
may be greatly reduced by increasing defects inside the fiber due
to aggregation of the metal catalyst remaining in the carbon
nanotube fiber when heat-treating a carbon nanotube fiber at
500.degree. C. or higher if there are many impurities.
[0056] Carbon nanotubes with a purity of 90% by weight or more may
be obtained by chemically purifying a carbon nanotube raw
material.
[0057] Chemical purification not only can control the purity of the
carbon nanotubes to 90% by weight or more, but also enables a
high-concentration liquid crystal spinning process to be performed
by functionalizing the carbon nanotube surface during the chemical
purification process, thereby improving dispersibility of the
carbon nanotubes. Through this, highly oriented, bundled fibers can
be manufactured, and since the gap between the carbon nanotubes is
narrowed so that the van der Waals force is increased, a carbon
nanotube fiber with more improved specific tensile strength and
specific tensile modulus can be provided.
[0058] After controlling the purity of the carbon nanotubes to 90%
by weight or more through chemical purification, a first carbon
nanotube fiber having a density of 0.6 g/cm.sup.3 or more, a
specific tensile strength of 0.5 N/tex or more, or 0.5 to 4.0
cN/tex, and a specific tensile modulus of 50 N/tex or more, or 50
to 250 N/tex may be obtained by spinning the purity-controlled
carbon nanotubes, and a second carbon nanotube fiber having
improved physical properties may be obtained by heat-treating the
first carbon nanotube fiber at 500.degree. C. or higher.
[0059] As a chemical purification method, for example, (i) it is
possible to treat the carbon nanotubes by using a strong acid such
as sulfuric acid, nitric acid, hydrochloric acid, etc. alone or by
using a mixture of the strong acid and hydrogen peroxide, ammonium
hydroxide (NH.sub.4OH), or the like. Further, the method may
comprise a process of removing the metal catalyst in the carbon
nanotubes by gas phase reaction of a halogen element compound such
as chlorine, fluorine, or the like. Processes combining these are
also possible.
[0060] A first carbon nanotube fiber having a density of 0.6
g/cm.sup.3 or more may be obtained by spinning carbon nanotubes
with a purity of 90% by weight or more.
[0061] The spun fiber may include a fiber obtained by wet spinning,
dry spinning, dry-wet spinning, or liquid crystal spinning.
[0062] The first carbon nanotube fiber may have a density of 0.6
g/cm.sup.3 or more, for example, 0.6 to 2.3 g/cm.sup.3, preferably
1.0 to 2.0 g/cm.sup.3. A carbon nanotube fiber having improved
specific tensile strength, specific tensile modulus, and
conductivity may be obtained through heat treatment continued in
the above range.
[0063] The first carbon nanotube fiber having a density of 0.6
g/cm.sup.3 or more may have an average diameter of 10 to 100
.mu.m.
[0064] According to an embodiment, the step of obtaining the first
carbon nanotube fiber having a density of 0.6 g/cm.sup.3 or more
may comprise a step of liquid crystal spinning or wet spinning a
dope containing the carbon nanotubes and a super strong acid.
[0065] A dope is prepared by dispersing the carbon nanotubes in the
super strong acid as a solvent. Although the super strong acid may
include, for example, one or more selected from chlorosulfonic
acid, sulfuric acid, fuming sulfuric acid, fluorosulfonic acid,
trifluoroacetic acid, trifluoromethanesulfonic acid,
fluoroantimonic acid (HSbF.sub.6), and carborane acid, it is not
limited thereto, and may include super strong acids or general
chemical solvents commonly used in the art. The dope may be
prepared by mixing purified carbon nanotubes and a super strong
acid to obtain a mixture, and then performing a process of
mechanically stirring the mixture. Mechanical stirring may be
performed in a stirring speed range of about 50 to 30,000 rpm.
[0066] The dope may have a carbon nanotube concentration of 5 to
100 mg/mL. Smooth spinning may be carried out in the above
range.
[0067] In the dope, the carbon nanotubes may exhibit a lyotropic
nematic phase, and these liquid crystal-forming properties may be
useful in increasing the mechanical, electrical, and thermal
properties of the obtained carbon nanotube fiber.
[0068] Prior to dope preparation, the carbon nanotubes may be
oxidized by heating the carbon nanotubes under an oxygen atmosphere
in order to increase dispersion of the carbon nanotubes in the
dope. For example, after oxidizing the carbon nanotubes by heating
the carbon nanotubes under an oxygen atmosphere in a range of 400
to 700.degree. C. for about 10 minutes to 8 hours, the oxidized
carbon nanotubes may be used in dope preparation.
[0069] The spun fiber may include a fiber obtained by wet spinning,
dry spinning, dry-wet spinning, or liquid crystal spinning.
[0070] In wet spinning, a filament-like first carbon nanotube fiber
may be obtained by allowing solidification due to diffusion of a
solvent to be proceeded while a discharged filament short fiber or
multiple fiber is passing through a coagulation bath with a length
of about 10 to 100 cm after directly spinning the dope, which is a
spinning undiluted solution, into the coagulating solution through
a spinneret immersed in a coagulating solution. Thereafter, the
first carbon nanotube fiber is wound on a winding roller.
[0071] In the case of dry-wet spinning, the spinneret is installed
in the air to be separated by a certain distance (for example, 1 to
100 mm, specifically 10 to 50 mm) from the surface of the
coagulating solution so that the filaments are allowed to be
immersed in the coagulating solution after moving the filaments by
a certain length in the air before filaments discharged from the
spinneret are immersed in the coagulating solution. In the case of
using dry-wet spinning, the filaments receive more tension than
those in wet spinning so that a fiber having high orientation
degree and density may be obtained.
[0072] In the case of dry spinning, processes of drying the bundled
fibers after bundling fibers synthesized through dry spinning using
a usual floating catalyst-chemical vapor deposition (FC-CVD) method
through a post-treatment process for bundling the fibers are
included.
[0073] In the spinning process, the dope, which is the spinning
undiluted solution, may be in a temperature range of about
20.degree. C. to about 100.degree. C., preferably about 30.degree.
C. to about 80.degree. C.
[0074] The coagulating solution is a non-solvent capable of
diffusing the solvent while solidifying the first carbon nanotube
fiber. A coagulation bath composition that can be used may include,
for example, the following systems: dimethyl ether, diethyl ether,
sulfuric acid, acetone, acetonitrile, chloroform, methanol,
ethanol, N-methylmorpholine-N-oxide (NMMO), dimethyl formamide
(DMF), N,N-dimethyl acetamide (DMAc), and dimethyl sulfoxide
(DMSO). These may be used alone or in combination of two or more
thereof as a coagulation bath. The coagulating solution is, for
example, 5% aqueous sulfuric acid solution, 96% sulfuric acid, DMF,
DMS, DMAc, or a mixed solution thereof.
[0075] Thereafter, a filament-like first carbon nanotube fiber
which has passed through the coagulating solution is washed with
water, and the filament-like first carbon nanotube fiber which has
been washed with water is drawn and wound while passing the
filament-like first carbon nanotube fiber through a hot water bath
and a thermal drawing furnace. The orientation of the carbon
nanotubes in the filaments is increased in the axial direction by
the winding tension of filaments during the spinning process, as
the filaments pass through the coagulation bath, solidification of
the filaments occurs so that the filaments are bundled again, and
densification of the filaments occurs, and manufacturing of the
first carbon nanotube fiber is completed by solidifying the
filaments in this state. At this time, the orientation degree and
density of the carbon nanotubes may be adjusted by adjusting a
ratio of the spinneret discharge speed and the winding roller
rotation speed (spin-draw ratio), that is, the tension. In general,
as the spin-draw ratio increases, the orientation degree and
density increase.
[0076] Stretching may be carried out at a ratio of 1.0 to 10.0, and
may be carried out, for example, at a ratio of 2.0 to 6.0. When
stretching is carried out in the above range, a first carbon
nanotube fiber having excellent specific tensile strength and
specific tensile modulus may be obtained.
[0077] After stretching, a cleaning process using a solvent such as
acetone or water may be performed. A step of drying a spun product
at a temperature of 200.degree. C. or less may be performed.
[0078] Subsequently, the method for manufacturing the carbon
nanotube fiber may obtain a carbon nanotube fiber (second carbon
nanotube fiber) which not only minimizes the gap between the carbon
nanotubes, thereby further increasing the density of the carbon
nanotubes to increase the van der Waals force, but also increases
the diameter of the carbon nanotubes to increase strength, etc. by
heat-treating a first carbon nanotube fiber at 500.degree. C. or
higher under an inert gas atmosphere.
[0079] The diameter of the carbon nanotubes may be increased by 2%
or more by heat treatment.
[0080] The heat treatment may be performed at 500.degree. C. or
higher under an inert gas atmosphere, and may be performed, for
example, at 500 to 3,000.degree. C., 1,000 to 2,700.degree. C., and
2,000 to 2,400.degree. C. Although the heat treatment time varies
depending on the heat treatment temperature, the heat treatment may
be performed, for example, for 1 to 60 minutes after reaching the
final temperature. The heat treatment may include continuous heat
treatment as well as batch-type heat treatment.
[0081] The heat treatment forms an inert gas atmosphere using an
inert gas including nitrogen, argon, helium, or a combination
thereof.
[0082] The heat treatment may include batch-type or continuous-type
heat treatment performed in a conventional heating furnace,
post-treatment such as Joule heating or microwave treatment for
performing heat treatment for a short time, and a combination
thereof. In addition, tension may be applied during heat
treatment.
[0083] A highly-densified carbon nanotube fiber may be obtained as
carbon nanotube fibers are bundled in the process of performing
heat treatment under the above-described conditions. Further, the
carbon nanotube fiber finally obtained through the Van der Waals
force or chemical crosslinking reaction may have increased specific
tensile strength and specific tensile modulus.
[0084] The second carbon nanotube fiber thus obtained may have a
density of 1.0 to 2.5 g/cm.sup.3, a specific tensile strength of
1.0 to 8 N/Tex, and a specific tensile modulus of 200 to 1,000
N/Tex, and a thermal conductivity of 100 to 2,000 W/mK.
[0085] The second carbon nanotube fiber thus obtained may have a
density of 1.5 to 2.5 g/cm.sup.3, a specific tensile modulus of 300
to 1,000 N/Tex, and a thermal conductivity of 200 to 1,500
W/mK.
[0086] At least a portion of the second carbon nanotube fiber is
graphitized, and may have a specific tensile modulus of 400 to
1,000 N/Tex and a thermal conductivity of 300 to 1,500 W/mK.
[0087] The carbon nanotubes of the second carbon nanotube fiber may
include 20 to 100% by weight of the double-walled carbon
nanotubes.
[0088] The carbon nanotube fiber obtained in the present disclosure
may be used as a functional composite material to be usefully
applied to next-generation new technologies and new materials such
as wearable devices, electric, electronic, and bio fields as well
as structural composite materials.
[0089] Exemplary embodiments are described in more detail through
the following examples and comparative examples. However, the
examples and comparative examples are for illustrating the
technical idea, and the scope of the present disclosure is not
limited thereto.
Comparative Example 1: Manufacturing of Carbon Nanotube Fiber
[0090] Carbon nanotubes used were single-walled carbon nanotubes
(SWCNTs) of Tuball.TM. (OcSiAl), and oxidation by heat was
performed on the carbon nanotubes at 600.degree. C. for 1 hour.
Chemical purification was additionally performed on the oxidized
carbon nanotubes in order to obtain carbon nanotubes with a high
purity. The carbon nanotubes oxidized by heat at 600.degree. C.
were purified while stirring the carbon nanotubes for 5 hours by
using a piranha (P) solution in which 98% sulfuric acid
(H.sub.2SO.sub.4) and 30% hydrogen peroxide (H.sub.2O.sub.2) were
mixed in a volume ratio of 7:3 as a purification solution. After
washing sufficiently the purified carbon nanotubes with distilled
water and acetone, the washed carbon nanotubes were dried in a
vacuum oven of 80.degree. C. for 12 hours or more.
[0091] A dope was prepared by dispersing the carbon nanotubes
purified as above to a concentration of 30 mg/mL in chlorosulfonic
acid (CSA). After dispersing the carbon nanotubes in the prepared
dope for one day or more, the prepared dope was spun using a
syringe. Spinning was performed using a needle having a diameter of
0.26 mm, and the fiber was spun in a state that the fiber had a
draw ratio of about 2.0 or more. A first carbon nanotube fiber
having a density of 1.5 g/cm.sup.3 was manufactured by using
acetone in both a coagulation tank and a water washing tank,
carrying out water washing for 2 hours, and finally drying the spun
fiber in a vacuum oven of 170.degree. C. for one day or more in
order to evaporate CSA inside the spun fiber.
Comparative Example 2: Manufacturing of Carbon Nanotube Fiber
[0092] A dope was prepared by dispersing carbon nanotubes
manufactured by Meijo Nano Carbon Co., Ltd in Japan to a
concentration of 8 mg/mL in chlorosulfonic acid (CSA). In EC-DX2
carbon nanotube used at this time, the weight ratio of
single-walled carbon nanotubes (SWCNTs) to double-walled carbon
nanotubes (DWCNTs) was 55:45. The carbon nanotubes used were
oxidized by heat at 400.degree. C. for 6 hours in order to increase
the dispersion effect. A first carbon nanotube fiber was
manufactured by using the same other conditions as in Comparative
Example 1.
Comparative Example 3: Manufacturing of Carbon Nanotube Fiber
[0093] A double-walled carbon nanotube (DWCNT) fiber was purchased
from DexMat.TM. in the United States.
Example 1: Manufacturing of Carbon Nanotube Fiber
[0094] The first carbon nanotube fiber manufactured according to
Comparative Example 1 was heat-treated using a heating furnace.
Since the first carbon nanotube fiber was oxidized during heat
treatment if air was present inside the heating furnace, the vacuum
was maintained to 10.sup.-3 torr before heat treatment, and
nitrogen or argon gas was filled inside the heating furnace.
Nitrogen was flown into the heating furnace at a rate of 20 sccm.
The heat treatment was performed by increasing the temperature to
about 1,400.degree. C. at a temperature increasing rate of 3 to
10.degree. C./min. A second carbon nanotube fiber was manufactured
by maintaining the temperature at a temperature of about
1,400.degree. C. for 30 minutes and cooling the first carbon
nanotube fiber naturally in a state in which nitrogen or argon gas
was flowing.
Example 2: Manufacturing of Carbon Nanotube Fiber
[0095] A second carbon nanotube fiber was manufactured in the same
manner as in Example 1 except that the heat treatment was performed
at 1,700.degree. C.
Example 3: Manufacturing of Carbon Nanotube Fiber
[0096] A second carbon nanotube fiber was manufactured in the same
manner as in Example 1 except that the heat treatment was performed
at 2,000.degree. C.
Example 4: Manufacturing of Carbon Nanotube Fiber
[0097] A second carbon nanotube fiber was manufactured in the same
manner as in Example 1 except that the heat treatment was performed
at 2,400.degree. C.
Example 5: Manufacturing of Carbon Nanotube Fiber
[0098] A second carbon nanotube fiber was manufactured in the same
manner as in Example 1 except that the heat treatment was performed
at 2,700.degree. C.
Example 6: Manufacturing of Carbon Nanotube Fiber
[0099] A second carbon nanotube fiber was manufactured by
manufacturing the first carbon nanotube fiber according to
Comparative Example 2 and performing the heat treatment in the same
manner as in Example 1.
Example 7: Manufacturing of Carbon Nanotube Fiber
[0100] A second carbon nanotube fiber was manufactured in the same
manner as in Example 6 except that the heat treatment was performed
at 1,700.degree. C.
Example 8: Manufacturing of Carbon Nanotube Fiber
[0101] A second carbon nanotube fiber was manufactured in the same
manner as in Example 6 except that the heat treatment was performed
at 2,000.degree. C.
Example 9: Manufacturing of Carbon Nanotube Fiber
[0102] A second carbon nanotube fiber was manufactured in the same
manner as in Example 6 except that the heat treatment was performed
at 2,400.degree. C.
Example 10: Manufacturing of Carbon Nanotube Fiber
[0103] A second carbon nanotube fiber was manufactured in the same
manner as in Example 6 except that the heat treatment was performed
at 2,700.degree. C.
Example 11: Manufacturing of Carbon Nanotube Fiber
[0104] A second carbon nanotube fiber was manufactured by
manufacturing the first carbon nanotube fiber according to
Comparative Example 3 and performing the heat treatment in the same
manner as in Example 1.
Example 12: Manufacturing of Carbon Nanotube Fiber
[0105] A second carbon nanotube fiber was manufactured in the same
manner as in Example 11 except that the heat treatment was
performed at 1,700.degree. C.
Example 13: Manufacturing of Carbon Nanotube Fiber
[0106] A second carbon nanotube fiber was manufactured in the same
manner as in Example 11 except that the heat treatment was
performed at 2,000.degree. C.
Example 14: Manufacturing of Carbon Nanotube Fiber
[0107] A second carbon nanotube fiber was manufactured in the same
manner as in Example 11 except that the heat treatment was
performed at 2,400.degree. C.
Example 15: Manufacturing of Carbon Nanotube Fiber
[0108] A second carbon nanotube fiber was manufactured in the same
manner as in Example 11 except that the heat treatment was
performed at 2,700.degree. C.
Evaluation Example 1: Transmission Electron Microscope (TEM)
Evaluation for Each Heat Treatment Temperature
[0109] Transmission electron microscope (TEM) images for each heat
treatment temperature of the single-walled carbon nanotube fibers
manufactured in Comparative Example 1 and Examples 1 to 5 are shown
in FIG. 1.
[0110] As shown in FIG. 1, the single-walled CNTs show strength
improvements of 1.8 to 2.1 times compared to before heat treatment
as single-walled CNTs merge with each other so that large-diameter
CNTs and collapsed CNTs are formed at 2,000.degree. C. or lower. It
is shown that CNTs start to change into the form of a graphitic
structure at 2,000.degree. C. or higher so that the specific
tensile strength decreases again. It is shown that the CNTs exist
in the form of the graphitic structure at 2,700.degree. C. so that
the elastic modulus and thermal conductivity increase by 1.3 times
and 1.19 times respectively compared to before heat treatment.
Evaluation Example 2: Transmission Electron Microscope (TEM)
Evaluation for Each Heat Treatment Temperature
[0111] Transmission electron microscope (TEM) images for each heat
treatment temperature of the carbon nanotube fibers in which the
ratio of single-walled CNTs to double-walled CNTs was 55:45
manufactured in Comparative Example 2 and Examples 6 to 10 are
shown in FIG. 2.
[0112] As shown in FIG. 2, CNTs with the ratio of the single-walled
CNTs to the double-walled CNTs of 55:45 show strength improvements
of 1.3 to 2.0 times compared to before heat treatment as the
single-walled CNTs merge with each other at 2,000.degree. C. or
lower so that large-diameter CNTs and collapsed CNTs are formed. It
is shown that the CNTs start to change into the form of a graphitic
structure at 2,000.degree. C. or higher so that the specific
tensile strength decreases again. It is shown that the CNTs exist
in the form of a graphitic structure without an empty space (pores)
at 2,700.degree. C. so that the elastic modulus increases by 2.9
times compared to before heat treatment.
Evaluation Example 3: Transmission Electron Microscope (TEM)
Evaluation for Each Heat Treatment Temperature
[0113] Transmission electron microscope (TEM) images for each heat
treatment temperature of the double-walled carbon nanotube fibers
manufactured in Comparative Example 3 and Examples 11 to 15 are
shown in FIG. 3.
[0114] As shown in FIG. 3, the double-walled CNTs show strength
improvements of 1.3 times compared to before heat treatment as the
diameter of a small amount of the single-walled CNTs is increased
at 2,000.degree. C. or lower. It is shown that the CNTs start to
change into the form of a graphitic structure at 2,000.degree. C.
or higher so that the specific tensile strength decreases again. It
is shown that the CNTs exist in the form of a graphitic structure
without an empty space (pores) at 2,700.degree. C. so that the
elastic modulus increases by 6.6 times compared to before heat
treatment.
Evaluation Example 4: Transmission Electron Microscope (TEM)
Evaluation for Each Heat Treatment Temperature
[0115] Graphs showing changes in CNT diameters for each heat
treatment temperature of the carbon nanotube fibers manufactured in
Comparative Examples 1 to 3 and Examples 1 to 15 are shown in FIGS.
4A to 6B.
[0116] As shown in FIGS. 4A and 4B, it can be seen that an increase
range in the CNT diameters increases as the heat treatment
temperature increases. It can be seen that, when the single-walled
CNTs are the majority, the diameters increase according to heat
treatment, whereas when the double-walled CNTs are the majority,
there are little changes in the diameters as shown in FIGS. 6A and
6B.
[0117] As shown in FIGS. 5A and 5B, it can be seen that, when the
single-walled CNTs and the double-walled CNTs are mixed at a ratio
of 55:45, diameters of the CNTs increase but do not significantly
increase.
[0118] When the heat treatment temperature is 2,400.degree. C. or
higher, the inside of the fibers loses the CNT form and changes
into the graphite form. Therefore, since the CNTs are almost
nonexistent at the corresponding temperature or higher, the
diameter of the CNTs is not indicated, but indicated by the
graphitic structure.
Evaluation Example 5: Measurement of Specific Tensile Strength,
Linear Density, Specific Tensile Modulus, Specific Electrical
Conductivity, and Thermal Conductivity
[0119] After measuring specific tensile strength, linear density,
specific tensile modulus, specific electrical conductivity, and
thermal conductivity of the carbon nanotube fibers manufactured
according to Examples 1 to 15 and Comparative Examples 1 to 3, the
measurement results are shown in Table 1 and FIGS. 7 to 9.
[0120] The above-described physical properties were measured using
FAVIMAT+ (short fiber property measuring instrument). This
equipment is equipment which measures tensile strength (N) and
linear density (tex) to calculate specific tensile strength
(N/tex).
[0121] FAVIMAT can calculate the linear density (p) by using the
equation
? = 1 2 ? .times. T .mu. .times. ? indicates text missing or
illegible when filed ##EQU00001##
using the natural frequency possessed by the fibers. Here, f is the
natural frequency [Hz], T is the tension [N], and L is the length
[km] of the fibers. After measuring the linear density in this
manner, the strength is measured through a tensile test. It is
equipment which can know the specific tensile strength by
calculating the measured strength and linear density.
[0122] Specific Tensile Strength (N/tex) is a value calculated
using the linear density calculated by FAVIMAT and the strength
(Force, N) measured in the tensile test.
[0123] Elongation also refers to the maximum elongation until the
fibers are broken through the tensile test of the fibers in
FAVIMAT. The elongation is represented by %.
[0124] Specific Tensile Modulus (N/tex) represents a slope in a
graph of the elongation and strength. Usually, the specific tensile
modulus indicates an initial slope value, and is indicated by
calculating a section in which the strength is constantly increased
according to the elongation.
[0125] Specific Electrical Conductivity (Sm.sup.2/kg) was
calculated according to the calculation formula by measuring the
resistance. After putting a silver paste on the carbon nanotube
fibers at 1 cm intervals, the resistance was measured. And then,
the linear density measured by FAVIMAT was calculated according to
cm/(.OMEGA.tex). Here, L is the measured length of the carbon
nanotube fibers.
[0126] Thermal conductivity (W/mK) was measured using one
dimensional self-heating method. After fixing the carbon nanotube
fibers to a substrate for measurement, a current was flown to the
carbon nanotube fibers in a high vacuum atmosphere to generate
Joule heat so that a temperature distribution was created in the
fibers. The temperature changes due to Joule heat of the fibers can
be measured by changes in the resistance of the fibers according to
the temperature. The average temperature increases of the fibers
due to Joule heat are represented by
.DELTA. .times. T = Q .times. L 1 .times. 2 .times. k .times. A ,
##EQU00002##
where Q is the Joule heat given to the carbon nanotube fibers.
Evaluation Example 6: Thermogravimetric Analysis for Each Carbon
Nanotube
[0127] After performing thermogravimetric analysis of the carbon
nanotubes used to manufacture the carbon nanotube fibers of
Comparative Examples 1 and 2, thermogravimetric analysis results
are shown in FIG. 10. The thermogravimetric analysis is a method of
quantitatively measuring the purity of the carbon nanotubes through
the remaining amount of the carbon nanotubes remained after
decomposing the carbon nanotubes by heat by setting the temperature
increasing rate in the air to 10.degree. C. per minute and
increasing the temperature to 900.degree. C.
[0128] As shown in FIG. 10, it has been confirmed as the
thermogravimetric analysis results that the single-walled carbon
nanotubes used in Comparative Example 1 had a purity of 95% by
weight or more, and the carbon nanotubes having the single-walled
carbon nanotubes and the double-walled carbon nanotubes used in
Comparative Example 2 mixed therein had a purity of 97% by weight
or more.
Evaluation Example 7: Density Measurement of Carbon Nanotube
Fibers
[0129] After measuring the density of the carbon nanotube fibers
manufactured according to Examples 1 to 15 and Comparative Examples
1 to 3, measurement results are shown in Table 1. A density
gradient tube, which is a method of measuring the extent to which
the fibers are located in the solvents due to the difference in
density by mixing two solvents having different densities, was
used. The density gradient tube is equipment which creates
environments with different densities within one solvent by mixing
benzene and tetrabromomethane solvent in an appropriate ratio. For
the corresponding density, the difference in density was
distinguished using reference beads for which the density had
already been known. After putting the carbon nanotube fibers in the
prepared solvent, the density was measured by observing the
position of the fibers after allowing the fibers to be left to
stand for at least 6 hours so that they could be accurately
positioned at the corresponding density.
TABLE-US-00001 TABLE 1 Specific Specific Heating tensile tensile
Elastic Thermal temperature strength modulus Strength modulus
conductivity Density (.degree. C.) (N/tex) (N/tex) (GPa) (GPa) (W/m
K) (g/cm.sup.3) Example 1 1400 1.16 137 1.53 181 -- 1.32 Example 2
1700 1.25 103 1.69 139 -- 1.35 Example 3 2000 1.31 172 1.73 227 --
1.32 Example 4 2400 0.50 162 0.82 264 -- 1.63 Example 5 2700 0.33
184 0.59 331 310 1.80 Example 6 1400 2.73 252 5.13 474 -- 1.88
Example 7 1700 4.25 368 7.01 607 437 1.65 Example 8 2000 2.93 322
4.63 509 -- 1.58 Example 9 2400 2.22 420 3.17 601 -- 1.43 Example
10 2700 1.53 445 2.89 841 490 1.89 Example 11 1400 1.34 83 2.47 153
-- 1.84 Example 12 1700 1.39 88 2.49 158 -- 1.79 Example 13 2000
1.54 89 2.63 152 -- 1.71 Example 14 2400 1.58 219 2.54 353 -- 1.61
Example 15 2700 1.24 535 2.43 1,049 500 1.96 Comparative -- 0.62
138 0.93 207 260 1.50 Example 1 Comparative -- 2.10 155 4.03 298
380 1.92 Example 2 Comparative -- 1.10 86 2.31 181 400 2.10 Example
3
[0130] According to the present disclosure, a carbon nanotube fiber
having improved physical properties and a method for manufacturing
the same are provided.
[0131] Although preferred embodiments according to the present
disclosure have been described with reference to the drawings and
examples in the above description, these are merely exemplary, and
those of ordinary skill in the art will be able to understand that
various modifications and equivalent other embodiments are possible
therefrom. Accordingly, the protection scope of the present
disclosure should be defined by the appended claims.
* * * * *